This invention relates to improvements in pressure domes used for coupling the blood pressure of a patient to a transducer that generates an electrical signal corresponding to the pressure. The domes are generally comprised of a body portion having ports extending therethrough so as to communicate with a cavity therein and a membrane that closes the open side of the cavity. Generally but not necessarily, the edge of the cavity to which the membrane is attached is circular. Use of the dome involves connecting a valve to a first port and connecting another valve between the second port and one end of a catheter. Both valves are opened and a suitable fluid is passed through the first port until both the cavity and the catheter are filled. The valve connected to the first port is then closed and the open end of the catheter is pushed through the arterial system until it reaches the point therein at which the pressure is to be measured. The dome is then attached to a pressure transducer in such manner that its membrane is brought into intimate contact with the pressure sensing surface of the transducer. With such an arrangement, the pressure in the blood at the open end of the catheter is conveyed via the fluid in the catheter and in the cavity to one side of the membrane and presses the other side of the membrane against the pressure sensing surface of the transducer so as to cause it to produce an electrical signal corresponding to the pressure.
Whereas the membrane of a pressure dome may be placed in contact with the pressure sensing surface of a transducer by screwing the dome and the transducer together, it was found that the contact pressure between the membrane and the pressure sensing surface of the transducer varied with the applied torque so as to require adjustment of the zero setting for each application. As described in U.S. Pat. No. 4,185,641, this problem was overcome by holding the dome and transducer together with a force determined by the tension of springs and arranging that the tension attain a given repeatable maximum value. Unfortunately, however, accidental forces occurring during handling or increases in the pressure of the fluid in the dome cavity can force the dome away from the transducer so as to permanently damage the springs by flexing them too far and/or permanently deform the membrane. In cases where the springs are obviously broken, the pressure dome can be replaced; but a more subtle and significant problem is the possibility that the springs can be weakened in a manner that is not readily noticed and thereby cause improper blood pressure readings, a zero shift, decreased temperature coefficient or dome dry-out.